This page documents two potential methods of migrating installed systems between i686 (32-bit) and x86_64 (64-bit) architectures, in either direction. The methods avoid reinstalling the entire system. One method uses a liveCD, the other modifies the system from within..

Warning: Unless explicitly stated, all these methods are UNTESTED and may irreparably damage your system. Continue at your own risk.

General preparation

Confirm 64-bit architecture

If you are already running x86_64 but want to install i686 this is not relevant and you can skip this step.

In order to run 64-bit software, you must have a 64-bit capable CPU. Most modern CPUs are capable of running 64-bit software. You may check your CPU with the following command:

grep --color '\<lm\>' /proc/cpuinfo

For CPUs that support x86_64, this will return the lm flag (“long mode”) highlighted. Beware that lahf_lm is a different flag and does not indicate 64-bit capability itself.

Disk space

You should be prepared for /var/cache/pacman/pkg to grow approximately twice its current size during the migration. This is assumes only packages that are currently installed are in the cache, as if “pacman -Sc” (clean) was recently run. The disk space increase is due to duplication between the i686 and x86_64 versions of each package.

If you have not enough disk, please use gparted to resize the relevant partition, or mount another partition to /var/cache/pacman.

Please do not remove packages of the old architecture from the cache until the system is fully operating in the new architecture. Removing the packages too early may leave you unable to fall back and revert changes.

Power supply

The migration may take a substantial amount of time, and it would be inconvenient to interrupt the process. You should plan on at least an hour, depending on the number and size of your installed packages and internet connection speed (although you can download everything before starting the critical part). Please make sure you are connected to a stable power source, preferably with some sort of failover or battery backup.

Fallback packages

If the migration fails halfway through, there are packages that can help sort out the situation, but they should be installed before the main packages are migrated. More details about using them under #Troubleshooting below.

One package is busybox, which can be used to revert changes. It is statically linked and does not depend on any libraries. The 32-bit (i686) version should be installed, using

# pacman -S busybox

Another package is lib32-glibc, from the Multilib x86_64 repository. It is probably only useful when migrating away from 32 bits; in any case you may safely skip this package. You can use the package to run 32 bit programs by explicitly calling /lib/ld-linux.so.2. Install with:

# pacman -S lib32-glibc

Method 1: Utilising the Arch LiveCD

Download, burn and boot the 64-bit Arch ISO LiveCD

Configure your network on the LiveCD, then pacman to use your new architecture repos

Method 2: From a running system

Ensure that your system is fully updated and functioning before proceeding.

# pacman -Syu

Package preparation

Cache old packages

Note: If you have any packages installed from the AUR or third-party repositories without new architecture availability, pacman will let you know it cannot find a suitable replacement. Make a list of these packages so you may re-install them after the update process and then remove them using pacman -Rsn package_name.

If you do not have all your installed packages in your cache, download them (for the old architecture) for fallback purposes.

# pacman -Sw $(comm -23 <(pacman -Qq|sort) <(pacman -Qmq|sort))

or use bacman from pacman-contrib package to generate them.

The command above redownload ALL packages, even the one already in the cache. This script only download the ones not in the cache:

If migrating to 32 bits, install the 32-bit Busybox fallback now that Pacman has been configured with the 32-bit architecture:

# pacman -S busybox

Warning: Don't install the lib32-glibc package now. After a ldconfig, when you install linux, the generated image will have libraries like librt.so in /usr/lib32, where binaries during boot won't search, resulting in a boot failure.

Package installation

Install kernel (64-bit)

Upgrading the kernel to 64 bits (x86_64) is safe and straightforward: 32 bit and 64 bit applications run equally well under a 64-bit kernel. For migration away from 64 bits, leave the 64-bit kernel installed and running for now and skip this step.

To install the standard Arch Linux kernel, use the following command:

# pacman -S linux

Now is the time to install the lib32-glibc fallback (you will need to add the [multilib] repository in pacman.conf if you have not already):

# pacman -S lib32-glibc

Note: If this fails due to an existing file of a differently named package, use pacman's -f flag.

Reboot and verify it is running the x86_64 architecture:

$ uname -m

x86_64

Console terminal

This is the time to switch to a text-mode virtual console (e.g. Ctrl+Alt+F1) for the rest of the process, if possible. Pseudo-terminals like SSH should work, but direct access is recommended as a precaution. There will be several packages removed and replaced during the update process that may cause X11 desktops to become unstable and leave your system in an unbootable state.

Install Pacman

Warning: Once you start updating pacman and its dependencies it can not be interrupted. Pacman and all of its dependencies must be installed at the same time in a single command line.

Use pactree to install Pacman and all its dependencies:

# pactree -l pacman | pacman -S -

Errors may be printed but they will not cause a problem as long as Pacman works. Immediately following this command only Busybox, Bash and Pacman will be executable until the other packages are migrated below. You must not reboot your system until the following commands have been completed. You have been warned.

Install remaining packages

Install all of the previously downloaded replacements for the new architecture. (Go get a drink and make a sandwich; this could take a while.)

# pacman -S $(pacman -Qq)

If some packages didn't install correctly, you should now be able to reinstall them successfully; if you're lazy, you can just re-run the last command to reinstall everything.

For migration away from 64 bits, you may want to skip installing a 32-bit kernel in the commands above, since the old 64-bit kernel will still run 32-bit programs.

After this step the migration in either direction should be complete and it should be safe to reboot the computer.

Cleanup

You are now free to remove Busybox and lib32-glibc.

# pacman -Rcn busybox lib32-glibc

Makepkg compiler flags

During the upgrade the new version of /etc/makepkg.conf may be stored as /etc/makepkg.conf.pacnew. You will have to replace the old version or modify it, if you want to compile anything with makepkg in the future.